Proportional throttle valves are often used when the level of the fluid flow passing through these valves is to be continuously changed as a function of a prevailing magnetic flow of a coil actuating the valve piston. With a slide valve, the opening cross section is dependent on the piston position. If the coil is supplied with an electrical current, a magnetic force proportional to the magnetic flow is generated. As a result of the magnetic force, the valve piston can be moved into an open position. A spring located on the back side of the valve piston is generally tensioned, with its spring force opposing the magnetic force. If an equilibrium is established between the magnetic force and the spring force, the valve piston remains in its position.
The proportional throttle valve is largely independent of the pressure level to be controlled because the valve piston is pressure-equalized by the pressure prevailing on the two end surfaces as well as in the pilot chamber.
Proportional throttle valves are used, for example, in lifting-lowering applications, such as in industrial trucks. In these applications, a 2/2 directional valve is typically used in the lifting-lowering motion for lowering the load. At the same time, proportional throttle valves are used to control the volumetric flow. To protect the entire system of these two valves, a pressure limiting valve is used in addition to limit the maximum pressure.
The known systems thus have a plurality of valves requiring the corresponding installation space.